Gauge control method for rolling mills and like apparatus



GAUGE CONTROL METHOD FOR ROLLING MILLS AND LIKE APPARATUS Filed Nov. 27,1967 2 Sheets-Sheet 1 F a =a4a(u F115 44 ,1; ckfllWEf-FECT INVENTOR.

Mme/s 0. $70M? Oct. 6, 1970 M. D. STONE 3,531,960

GAUGE CONTROL METHOD FOR ROLLING MILLS AND LIKE APPARATUS Filed Nov. 27,1967 2 Sheets-Sheep 2 INVENTOR. MORE/.5 0. 570? ATTOIPA/EV.

Patented Oct. 6, 1970 3,531,960 GAUGE CONTROL METHOD FOR ROLLING MILLSAND LIKE APPARATUS Morris Denor Stone, Pittsburgh, Pa., assignor toUnited Engineering and Foundry Company, Pittsburgh, Pa., a corporationof Pennsylvania Filed Nov. 27, 1967, Ser. No. 685,758 Claims priority,application Great Britain, Dec. 15, 1966, 56,166/ 66 Int. Cl. B21h 37/08US. Cl. 728 6 Claims ABSTRACT OF THE DISCLOSURE The present inventionrelates to a method of compensating simultaneously for variations in theroll gap and the effective crown of a roll in a rolling mill or likeapparatus, incident to a change in the rolling load, by imposing abending moment on at least one of the rolls of the mill in a directionand of a magntiude to correct for longitudinal variations andadvantageously effect transverse variations.

This invention relates to a method of processing striplike material,such as, steel or rubber, and, more particularly, to obtaining constantthickness in the longitudinal dimension and constant profile or crown inthe transverse dimension of the material.

BACKGROUND OF INVENTION In the reducing of the thickness of strip-likematerial, for example, metallic strip processed in a rolling mill, it isextremely important to maintain both the longitudinal and transversethickness within close tolerances. As used herein, the term gauge ismeant to mean the thickness of the material at any point longitudinallyor laterally of the strip, i.e., the point thickness of the material-notan average thickness across a given section of the material. Heretofore,the method and apparatus designed to correct for gauge variation in thelongitudinal direction or dimension, such as, US. Pat. No. 2,726,541which issued on Dec. 13, 1955 does not correct or advantageously affectthe gauge in the transverse direction. Conversely, the method andapparatus designed to correct for transverse gauge variation, forexample, by bending the rolls, which is exemplified in US. Pat. No. 3,250,- 105 which issued on May 10, 1966, does not correct for longitudinalvariation.

Accordingly, this requires the employment of separate and distinctequipment to undertake the correction of gauge variation in the twodirections or dimensions. In practice the expense is prohibitive and, asa result, generally, only one correction system is employed in a givenmill. In one known mill where both systems were employed it wasnecessary to develop a third system that would correct the fact that, inhandling the rolls to control the transverse gauge, objectionablechanges were made in the roll gap due to imposing additional stretch onthe mill which affected the desired longitudinal gauge. Accordingly, thethird system was designed repositioning the mill screws to oflset theadverse effect.

In the past, when equipment was used to correct for variation intransverse thickness, no attempt was made to use the equipment tocorrect for longitudinal gauge variation as an inherent function of thetransverse gauge variation correcting system.

The present invention relates to a method of controlling the thicknessof strip-like material both transversely and longitudinally asdetermined by the gap between a pair of rolls and wherein roll bendingmeans are provided to bend the neck portions thereof and thus displacethe roll bodies to vary their relative positions to thereby control thelongitudinal thickness of the material and to bend the roll bodies tovary their crowns to thereby control the transverse thickness of thematerial, and comprises the steps of:

Detecting a change in the roll gap of the mill caused by a change in therolling pressure between the rolls, and

Varying the degree of the displacement and bending of at least one ofsaid rolls pursuant to the detected change in the roll gap to controlthe relative position of the roll bodies and the crown of said one roll.

The present invention, in one form, relates to a method of operating a4-high rolling mill, including bending means associated with the backuprolls thereof adapted to impose bending moments on the backup rolls tocause the rolls and, hence, their associated work rolls to be displacedand bend in a vertical plane containing the axes thereof, thereby, tochange the relative position of the bodies of the work rolls and alsotheir effective crowns, and comprises the steps of:

Producing a signal representing a change in average rolling load of thematerial being rolled which will cause a variation in the roll gap ofthe mill, and

Varying the magnitude of the bending moments pursuant to said signal todisplace and bend the backup rolls and, hence, their associated workrolls to obtain constant thickness in the longitudinal dimension andconstant crown in a transverse dimension of the material being rolled.

These features, as well as others, can be better appreciated from thefollowing description when considered along with the accompanyingdrawings of which:

FIG. 1 is a schematic elevational view of a 4-high roll-. ing mill forpracticing one form of the present invention;

FIGS. 2a and 2b are schematic views of the housings and upper backuproll, respectively, illustrated in FIG. 1; and

FIG. 3 is a typical control circuit for the mill shown in FIG. 1.

In FIG. 1 there is shown a 4-high rolling mill quite similar inconstruction and operation to the mill illustrated in theabove-mentioned US. Pat. No. 3,250,105. US. Pat. No. 3,171,305 whichissued on Mar. 2, 1965 illustrates a somewhat different form of mill towhich the present invention may be applied. The mill illustrated in FIG.1 follows a well-known construction comprising a pair of housings 11 and12, the housings having windows for the reception of cooperative pairsof backup and work rolls 13 and 14, respectively. The upper backup rollis positioned by a pair of driven screws 15 and 16. In addition, thebackup rolls are adapted to be deflected by piston cylinder assemblies17 and 18, for which purpose the rolls are provided with extended necks19 between which the piston cylinder assemblies are mounted, each havingtwo opposed pistons contacting the necks 19. The piston cylinderassemblies 17 and 18 are operated under pressure to deflect the rolls 13and 14 to thereby control the magnitude of the relative displacement andbending of the roll bodies of the work rolls 14. Since these elements asother components of the mill are well known, as exemplified in theabove-noted patents, further description and reference are not deemednecessary.

The present invention is the result of a discovery that the relativedisplacement and crown of the rolls of a mill or like device can beappreciably and effectively controlled by controlling the deflection ofat least one of the rolls. More particularly, the discovery illustratesthat the relative displacement of the work rolls of a 4-high mill can becontrolled by the deflection of a backup roll and at the same time, theeffective crown of the work rOlls can be advantageously affected tocompensate for the results of a change in the rolling load which wouldotherwise detrimentally affect the gauge of the strip in both alongitudinal and transverse direction. The importance of this is thatnot only can the longitudinal gauge of the material be controlled, butat the same time, and by one and the same means, the shape or contour ofthe strip can be improved. It is to be remembered that in the rollingprocess as the rolling pressure varies, the distance between the rollsvaries-this change affecting the longitudinal thickness of the strip andat the same time varying the contour or profile of the strip. The centerof the strip has a tendency to become thicker with an increase in therolling pressure and thinner with a decrease thereof. As earlier noted,the present invention discloses a method whereby, in correcting for achange in the longitudinal thickness of the strip, at the same time andas an inherent function thereof, it provides for changing the contour ofthe rolls in the manner to offset the aforementioned change in thecontour of the strip.

This accomplishment may be better understood by referring to an actualrolling condition. In FIGS. 2a and b, there is illustrated inexaggerated form the relationship between the bending of the backuprolls 13 and the stretch of the housings under the forces S of the rollbending cylinders 17 and 18. The relation between the thickness of stripbeing rolled in such a mill (or the loaded roll gap of the mill) and thevarious mill parameters can be written as:

1 i, [M....1] [M... MBURB] where Due to changes in either h P, or F, theconsequent change in gauge is, therefore:

1 1 1 At=Ah API: AFl:2(--)] mill M1185 MBURB For instance, if it isdesired to determine how much the gauge Would change as a result of achange in F by an amount, AF, with P and 11 unchanged (i.e. AP=0 andAll=0), the following equation applies:

(M1155 BuuB A change in the housing stretch is denoted as A whereby AFhsg hiig Similarly, a change in roll body displacement is denoted as AWhere BU MBURB The value A is contributed to by two principal millcomponent deformations (1) (S and (2) 6 where, 6 is the bending of thein-board backup roll necks between the main housings and the roll body,and 6, is the bending of the backup roll body itself. The values of aand 6, and, hence, A are given by the following equations:

a moment arm of bending force, F (in.) E=modulus of elasticity (lbs/in?)h distance from main bearing to roll body (in.) l=length of roll body(in.)

I =moment of inertia of in-board roll neck (infi).

1 1 1 EEEJ (Mm-m9] 1 AF mill (for constant gauge) MBURB hsz Now,substituing Eq. 6c in eq. 5, the following is derived:

2E MBURB=a" [ZIf+hl+l2/6] n b It is also to be recognized that theincrease in mill crown due to backup roll bending, is given by:

A numerical example of a 26" x 58" X 144" 4-high mill brings out themagnitudes involved.

Thus:

I =555,000 in.

I =40,000 inf 1:144", 11:25", and a:50"

M 16 lbs/in.

M =42 16 lbs./in., calculated from Equation 8.

Let it be assumed now that the mill is rolling a given product and thatthe entering thickness increases, so an increase in rolling pressure ofAP=5O O,OOO is required to maintain the delivery gauge constant. To dothis automatically, Equation 7 dictates that the ratio of AF/AP must bekept constant by increasing the hydraulic pressure and that for thismil, this ratio is Increase in mill crown due to BURB=25 42X l0 lOOX 1O=1.07 (for constant gauge) and so, AF (required) :l.07 500,000=535,000#at each end of the backup rolls.

At the same time that the gauge is being maintained constant, despite arequired increase in rolling load of 500,000#, the crown of the mill isbeing increased according to Equation 9 by Increase in mill crown (dueto BURB) (AF)al 535,000 50 (144) 4E1 4 30 10 555,00O

The immediate advantage of the present form of gauge control method isfound in the fact that the correction effected by the roll bendingcylinders is extremely rapidof the order of .1 second or less; whereinin the presentday correction screwdown systems the time is of the orderof 1 to 2 seconds, resulting in a relatively long lap time between thetime an error is discovered and correction is made. This, of course,produces substantial elf-gauge material. In the present invention thecorrection is effected almost instantaneously.

With reefrence now to FIG. 3 which illustrates a typicalelectrical-hydraulic circuit for practicing the present invention and,particularly, in reducing automatically any gauge error to zeroaccording to the following formula:

where e=gauge error t=desired thickness t'=actual thickness,

the other terms having been previously identified.

It will be appreciated that the reduction of the error in accordancewith the Equation 10 is based upon the relationship set out in Equation7, in which the relationship between the AF and AP is held constant whenthe error is made to be zero.

The control circuit illustrated in FIG. 3 is designed to solve Equation10. The value P being derived from the load cell 21, the value from apressure transducer 22 connected to the cylinders 17 and 18, the value hfrom a potentiometer 23 coupled to the mill screws 15 and 16 (in FIG. 3the potentiometer 23 is shown coupled to a motor 24 that drives the milscrews), the required material gauge 1 is set up on a manual controlpotentiometer 25. Electrical signals representing h l/M l/M I/M and tare summed in a summing circuit 26 to produce an error signal e, whichis amplified in amplifier 27 and sent to a differentiating circuit 28,the difference signal being applied to a pressure control valve 29 in asupply line 31 of the cylinder to reduce the error signal to equal zero.

In accordance with the provisions of the patent statutes, I haveexplained the principle and operation of my invention and haveillustrated and described what I consider to represent the bestembodiment thereof. However, I desire to have it understood that withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

I claim:

1. A method of simultaneously controlling the longitudinal andtransversal thickness of strip material as determined by a gap formedbetween a pair of reducing roll means, either or both of which may besupported by backup roll means, at least one of said roll means havingextended neck portions comprising the steps of:

detecting a change in the roll gap caused by a change in the reducingpressure between the rolls, applying a bending force to said extendedneck portions of at least one of said reducing roll means or backup rollmeans so as to both displace the body of the roll means by virtue of thebending of said neck portions to vary the relative position of thereducing roll means with respect to the other of said reducing rollmeans and thereby elfect a change in the roll. gap resulting in a changein the longitudinal thickness of the material and to bend the roll bodyof said one reducing roll means or backup roll means to vary its contourand thereby effect a corresponding change in the shape of the roll gapresulting in a variation in the transverse thickness of the material,and

varying the degree of displacement and bending of said one roll meanspursuant to a detected change in the roll gap caused by a change in thereducing pressure to control the position and contour of said one rollmeans.

2. A method of controlling the roll gap of a rolling mill or likeapparatus in a manner to simultaneously correct for variations in thelongitudinal and transversal dimensions of the material beingrolled,wherein said rolling mill includes a housing, a pair ofcooperative rolls received in said housing adapted to form a roll gapinto which the material passes, the steps comprising:

measuring the rolling force created between the rolls by the materialpassing therebetween,

applying a bending force on at least one of said rolls to both displacesaid one roll relative to the other roll to effect a change in thelongitudinal gauge of the material and to bend the roll body of the saidone roll to vary its contour to effect a change in the transverse gaugeof the material, and

varying the bending force applied to said one roll as a result of achange in the rolling force so as to maintain the ratio between thebending force and the rolling force constant.

3. A method of controlling the roll gap of a rolling mill and likeapparatus in accordance with claim 2 comprising the additional step of:

' applying a bending force to said other roll of equal magnitude and inthe direction opposite to said one roll.

4. In a method of controlling the roll gap of a rolling mill or likeapparatus in a manner to simultaneously correct for variations in thelongitudinal and transversal dimensions of material being rolled,wherein said rolling mill comprises a housing, a pair of work rolls anda supporting backup roll for each working roll, all received in saidhousing, said work rolls forming a roll gap into which the material ispassed, the steps comprising:

establishing an initial roll gap between said work rolls prior to thematerial entering between said rolls, measuring the rolling forcecreated between said work rolls by the material passing therebetween,

applying a bending force to at least one of said backup rolls to bothdisplace said backup roll relative to said other backup roll to allow acorresponding displacement of the work rolls to efiect a change in thelongitudinal "gauge of the material and to bend the roll body of thebackup roll to vary its contour to cause a corresponding change in thebody of the associated work roll to effect a change in the transversegauge of the material, and

varying the bending forces applied to said backup roll so as to maintainthe ratio between the bending forces and the rolling force constant.

5. A method of controlling the longitudinal thickness of strip materialas determined by a gap formed between a pair of reducing rolls, eitheror both of which may be supported by backing up rolls, comprising thesteps of:

detecting a change in the roll gap caused by a change in the reducingpressure between the rolls,

applying a bending force to at least one of said reducing rolls orbacking up rolls so as to displace the body of said one roll to vary itsrelative position with respect to the other of said reducing rolls andthereby effect a change in the roll gap to effect a change in thelongitudinal thickness of the material,

varying the degree of displacement of said one roll pursuant to adetected change in the roll gap caused by a change in the reducingpressure to control the position of said one roll.

7 8 6. A method of controlling the longitudinal thickness 3,250,1055/1966 Stone 72-245 of strip material in accordance with claim 5, theaddi- 3,442,109 5/ 1969 Diolot 72240 tional step of applying a bend ngforce to only the bacl FOREIGN PATENTS mg up rolls to vary theirrelative positions, and the positions relative to each other of theirassociated reducing 684,156 19 Canada. rolls to effect a change in theroll gap. 9 747,347 956 Great Brltaln.

Refer n s Cit d MILTON S. MEHR, Primary Examiner UNITED STATES PATENTSUS. Cl. X.R. 2,897,538 8/1959 Shapiro et al. 72245 10 72245 3,171,3053/1965 Stone 72-245 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No 3 ,531 ,960 October 6 1970 Morris Denor Stone It iscertified that error appears in the above identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4 I lines 51 to 53 the equations should aopear as shown below:

6 M 100 X 10 lbs ./1n M 34 x 10 lbs ./in

mill 6 MBURB 42 x 10 lbs ./1n, calculated from Equation 8.

same column 4, line 61 and column 5, line 43, "'mil", each occurrecne,should read mill Column 5, line 12, "lap" should read lag H line 17,"reeference" should read reference Signed and sealed this 30th day ofMarch 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, JR.

Attesting Officer Commissioner of Patents

